Just have it drywalled to the ceiling and eliminate the threat. If you think this is something your littlest one will outgrow, then I might just have railing to match the stair rail ( but higher so there isn’t the attraction to climb over it!!).

Definitely Take out the railing upstairs and drywall to the ceiling and add a gate upstairs at the entrance to the stairs , then pray ...or put the children's rooms downstairs .

I guess drywall is the safest answer it is interesting with that stairwell but safety first . My sister and I used the railing to slide down instead of the stairs I guess my point is there is no way to make a staircase perfectly safe.